Except for the fact that the main characters' names are Wren, Reynold, Everett and Lucy nothing, and I repeat NOTHING is even remotely relevant from the game of the same name. The characters are supposed to be 5 year olds, but here they are 12 year olds. Why? I guess the director of this show has a 12 year old son/daughter, and he/she treats the son/daughter like a little child (like how Lucy's mother treats her). That's why the show thinks it's cute to show the children to behave like little kids. It's completely out of place.
The kids wear their Halloween costumes all year round, no matter which day it is. They don't even go to school. It could have been understandable if they did this during the day of Halloween like how it was in the game, but how could they have churned out the big bucks if the show ended so quickly? The show also seems to really hate teenagers, by portraying them all as nerds. Also what was with all this Abe Lincoln Jr thing? There was no such thing in the entire game. It seemed like a plot just brought in to stretch the show for as long as possible. In the last 3 episodes it finally looked like something big was going to happen, but the final episode ruined the whole thing.
All the characters behave nothing like their game counterparts. Even their costumes are wrong. Wren is supposed to wear the robot costume (considering she is the brave one here and Reynold is the coward), Everett wears a knight costume which isn't even shown in this entire show, Lucy wears a Statue of Liberty costume and Reynold wears a candy costume on which the entire plot of Costume Quest took place in the game. Lucy is the one character this show completely butchered. Why on earth does Lucy keep calling Wren as "Mama Wren"? Is she her daughter? Or is this something people do in real life? In the game Lucy is supposed to be a nerd who knows a lot about science and maths, but here she's just a polite child. Even her mother is a racist stereotype of Asian mothers.
Speaking of mother, if they really wanted to show parents in this cartoon they could have shown Wren and Reynold's parents like it was in the game. So many characters were missing and replaced. Cadaverous Big Bones, Dorsilla, all the monsters other than Grubbins, none of them were used. Instead they showed this guy called Bob, who didn't even pose as big of a threat as Dorsilla did (and that's actually saying something because she was the second in command of the bad guy). In PewDiePie's words, "So who the hell is Bob and why you wanna kiss him?" Even Grubbins look nothing like the games. They just look like generic ugly monsters shown in every cartoon.
And finally the elephant in the room - The animation. It's so horrendous! It's like all these "new age" American cartoons that come on TV nowadays and kids have to tolerate just because there is nothing better to watch. They could have just copied the game's art style. They looked so cute in them. Here they look like bobbleheads. It looks like they were just asked to make a cartoon so they made the most generic thing they could possibly think of and slapped the name "Costume Quest" on it so that it becomes a selling point.
There's no thinking twice that this is an atrocity, and that's actually saying something because I have never given a 1 star rating to any of my previous 87 reviews (the minimum I have given until now is 2). You know how bad it is when Wikipedia, Rotten Tomatoes, Metacritic or even Google User Reviews don't have a page for it. And I'm really glad that when we look up Costume Quest on Google, the game is the first thing that comes up. It has restored my faith in humanity. The only reason why this show is on this website is because it's an Amazon Original, and I'm really thankful that I rant over it here.